The road to the red sequence: A detailed view of the formation of a massive galaxy at z~2

Understand

(Abridged) We present here a detailed analysis of the star formation history (SFH) of FW4871, a massive galaxy at z=1.893+-0.002.

• We compare rest-frame optical and NUV slitless grism spectra from the Hubble Space Telescope with a large set of composite stellar populations to constrain the underlying star formation history.
• Even though the morphology features prominent tidal tails, indicative of a recent merger, there is no sign of on-going star formation within an aperture encircling one effective radius, which corresponds to a physical extent of 2.6 kpc.
• A model assuming truncation of an otherwise constant SFH gives a formation epoch zF~10, with a truncation after 2.7 Gyr, giving a mass-weighted age of 1.5 Gyr and a stellar mass of 0.8-3E11Msun, implying star formation rates of 30-110 Msun/yr.